Add support for AVX512 registers

Unlike the SSE and AVX registers, the AVX512 registers appear to be used
exclusively in 32- and 64-bit mode. There are no instructions to operate
on 8- and 16-bit quantities; instead, there are instructions to do zero-
and sign-extension on load and truncation and saturation on store.

Change-Id: I0cd07a72e3aeb74f68c36d64cabc420711e51372
Reviewed-by: hjk <hjk121@nokiamail.com>